5:15 PM - 6:45 PM
[PPS01-P07] Modeling the distribution of CO2 on Europa: Implications for an active supply of CO2 ice
Recent James Webb Space Telescope (JWST) observations have uncovered the presence of CO2 ice scattered around Tara Regio on Europa, suggesting an endogenic source for the CO2 (Trumbo et al., 2023). This observation hints at an active CO2 supply originating from Tara Regio, yet the precise timescale of this supply remains elusive. In this study, we delve into the distribution and longevity of CO2 ice on Europa by employing Monte Carlo simulations to trace the transport of CO2 molecules.
Our model of CO2 transport encompasses processes such as release via sublimation, atmospheric flight, and re-trapping on the surface (Palmer & Brown, 2008; Zhang & Paige, 2009). We posit the source of CO2 molecules to be located at 10oS, 70oW, corresponding to the center of Tara Regio.
Monte Carlo simulations were conducted to explore various parameters, including exposure timing at the CO2 source, initial velocity, and residence time between re-trapping and release. We assumed a uniform distribution for exposure timing, an isotropic distribution for initial velocity direction, and a Maxwell distribution for speed. The residence time followed an exponential distribution, with the parameter determined by the sublimation rate of CO2 ice at the given temperature.
For simplicity, we assumed a ballistic trajectory for CO2 transport within Europa's atmosphere, neglecting any traps within the regolith or rough surfaces and assuming a smooth surface. The annually averaged surface temperature was estimated using an energy balance model (Ashkenazy, 2019).
Due to the dependence of residence time on surface temperature, CO2 molecules at lower latitudes experience more frequent transport than those at higher latitudes. For instance, the average residence time at the equator is approximately 10 ms due to the higher surface temperature (~100 K), whereas at the polar regions (~30 K), it exceeds 10 Gyr. Consequently, CO2 molecules would gradually shift to the higher latitudes. After one year, a CO2 molecule would be in the region of > 60o, 70o, and 80o with a probability of 99.7%, 99.5%, and 80.6%.
Assuming an infinite source of CO2, we observed an increase in CO2 ice concentration in polar regions over time, while the distribution of CO2 within lower latitudes (<60o) reached a steady state within one year. At low latitudes, CO2 ice concentrated around the source (10oS, 70oW), diminishing with distance. This distribution aligns with JWST observations (Trumbo & Brown, 2023).
The estimated lifetime of CO2 in low latitude regions (~1 year) suggests an active supply of CO2 ice occurring within several years. However, processes like CO2 trapping in the regolith or rough surfaces could lengthen timescales. Additionally, CO2 accumulation in polar regions (>70o) may be observable by probes in polar orbits despite not being detected by JWST observations.
Our model of CO2 transport encompasses processes such as release via sublimation, atmospheric flight, and re-trapping on the surface (Palmer & Brown, 2008; Zhang & Paige, 2009). We posit the source of CO2 molecules to be located at 10oS, 70oW, corresponding to the center of Tara Regio.
Monte Carlo simulations were conducted to explore various parameters, including exposure timing at the CO2 source, initial velocity, and residence time between re-trapping and release. We assumed a uniform distribution for exposure timing, an isotropic distribution for initial velocity direction, and a Maxwell distribution for speed. The residence time followed an exponential distribution, with the parameter determined by the sublimation rate of CO2 ice at the given temperature.
For simplicity, we assumed a ballistic trajectory for CO2 transport within Europa's atmosphere, neglecting any traps within the regolith or rough surfaces and assuming a smooth surface. The annually averaged surface temperature was estimated using an energy balance model (Ashkenazy, 2019).
Due to the dependence of residence time on surface temperature, CO2 molecules at lower latitudes experience more frequent transport than those at higher latitudes. For instance, the average residence time at the equator is approximately 10 ms due to the higher surface temperature (~100 K), whereas at the polar regions (~30 K), it exceeds 10 Gyr. Consequently, CO2 molecules would gradually shift to the higher latitudes. After one year, a CO2 molecule would be in the region of > 60o, 70o, and 80o with a probability of 99.7%, 99.5%, and 80.6%.
Assuming an infinite source of CO2, we observed an increase in CO2 ice concentration in polar regions over time, while the distribution of CO2 within lower latitudes (<60o) reached a steady state within one year. At low latitudes, CO2 ice concentrated around the source (10oS, 70oW), diminishing with distance. This distribution aligns with JWST observations (Trumbo & Brown, 2023).
The estimated lifetime of CO2 in low latitude regions (~1 year) suggests an active supply of CO2 ice occurring within several years. However, processes like CO2 trapping in the regolith or rough surfaces could lengthen timescales. Additionally, CO2 accumulation in polar regions (>70o) may be observable by probes in polar orbits despite not being detected by JWST observations.